1. Field of the Invention
The present invention relates to a slide drive unit of a press, which more specifically relates to a slide drive unit with improved slide motion.
2. Description of Related Art
Conventionally, a slide drive unit of a link press slowly lowers and quickly raises a slide, an example of which has been shown in Japanese Examined Patent Publication No. Sho 47-7835.
The slide drive unit has: a main gear rotated around a main gear supporting fixed shaft; a double-arm link and a single-arm link rotatably fitted to an eccentric drum integrated with the main gear; a connecting rod connected to an end of the double-arm link; an intermediate link connected to the other end of the double-arm link; and a triaxial link rotated around another fixed shaft parallel to the main gear supporting fixed shaft and connected to the intermediate link and the single-arm link, the fixed shaft and the other two shafts (connected with the intermediate link and the single-arm link) of the triaxial link being located approximately on a straight line extending approximately perpendicular with the fixed shaft at the center thereof.
Since deep-drawing formability is attached so much importance in the slide drive unit that slide motion in lowering the slide becomes too gentle, the difference between crank angle where the slide is located at a height above the bottom dead center and crank angle at the bottom dead center is substantially great. Accordingly, the slide reaches at a low position at an early stage before the bottom dead center.
Incidentally, a transfer press is ordinarily continuously driven without stopping at the top dead center per one operation cycle as in a single press and a tandem press, and SPM (cycle per a minute) tends to increase for improving productivity, where the time per one cycle may be two to three seconds.
When the above-described slide drive unit is applied to the transfer press, since the slide reaches to the low position at a too early stage, the time reserved for conveyance of a workpiece with a transfer bar is further shortened and feed motion of the transfer bar is strictly limited. Accordingly, high-speed drive of the transfer feeder is required.
However, when the transfer feeder is driven at a high speed without changing the feed motion, great acceleration and deceleration is applied on the transfer bar, thereby easily causing misfeed of a workpiece. Therefore, there is inherent limit for increasing the speed of the transfer feeder. Though a workpiece may be securely conveyed while causing small acceleration and deceleration on the transfer bar by adjusting the feed motion, the conveyed workpiece is likely to interfere with the die in this arrangement, so that die design becomes difficult.
In order to reduce acceleration and deceleration generated on the transfer bar while overcoming the restriction on the die to improve the productivity of a press, longer time has to be retained for conveying the workpiece, and slide motion therefor has been desired.
An object of the present invention is to achieve a slide motion of a slide drive unit of a press capable of improving the productivity of a press and prolonging the time for conveying a workpiece.
A slide drive unit of a press according to an aspect of the present invention includes: a main gear; a double-arm link and a single-arm link rotatably fitted to an eccentric drum integrated with the main gear; a connecting rod connected to one end of the double-arm link; an intermediate link connected to the other end of the double-arm link; and a triaxial link rotated around a fixed shaft parallel to a main gear supporting fixed shaft for supporting the main gear, the triaxial link being connected with the intermediate link and the single-arm link, in which an angle formed by a straight line connecting a connecting shaft of the intermediate link with the fixed shaft of the triaxial link and another straight line connecting the connecting shaft of the single-arm link and the triaxial link and the fixed shaft of the triaxial link is acute.
According to the above aspect of the present invention, the angle formed by straight lines connecting a fixed shaft and two connecting shafts of a triaxial link is set acute, so that position of a slide at any crank angle can be made higher than a conventional arrangement throughout the entire slide motion, where the time for, for instance, the slide to be lowered from the top dead center to a predetermined position can be lengthened. Accordingly, the slide can be located above a height necessary for conveying a workpiece for a longer time per the same SPM, thereby driving a transfer feeder with sufficient time. Therefore, the workpiece can be securely conveyed without causing great acceleration and deceleration to a transfer bar etc. and restricting die design even when the productivity of the press is enhanced.
In the above arrangement, one end of the connecting rod may preferably be connected to the double-arm link and the other end of the connecting rod may preferably be connected to the slide or a plunger perpendicularly reciprocating between the connecting rod and the slide, and wherein horizontal position of a center of a shaft connecting the other end of the connecting rod may preferably be shifted to a side opposite to the fixed shaft of the triaxial link relative to a shaft center of the main gear supporting fixed shaft. With the above arrangement, only compressive force is applied to the single-arm link or the intermediate link while driving the slide, so that shaky movement at the connecting shaft of the respective links caused by switching force such as alternately applied compressive force and tensile force is unlikely to be caused, thereby improving processing accuracy.